The present invention generally relates to environmental control systems, such as heating, ventilation, and air conditioning (HVAC) systems, which can be used to control the temperature and/or humidity of common spaces, e.g., as can exist in data centers containing server computers. More specifically, embodiments of the present invention relate to controlling multiple HVAC units in a stable and efficient manner.
Modern datacenters use HVAC systems to control indoor temperature, humidity, and other variables. It is common to have many HVAC units (often referred to as computer room air conditioner (CRAC) in the data center context) deployed throughout a data center. They are often floor-standing units, but may be wall-mounted, rack-mounted, or ceiling-mounted. The HVAC units also often provide cooled air either to a raised-floor plenum, to a network of air ducts, or to the open air of the data center. The data center itself, or a large section of a large data center, typically has an open-plan construction, i.e. no permanent partitions separating the air in one part of the data center from the air in another part. Thus, in many cases, these data centers have a common space is temperature-controlled and humidity-controlled by multiple HVAC units.
HVAC units for data centers are typically operated with decentralized, stand-alone controls. It is common for each unit to operate in an attempt to control the temperature and humidity of the air entering the unit from the data center. For example, an HVAC unit may contain a sensor that determines the temperature and humidity of the air entering the unit. Based on the measurements of this sensor, the controls of that HVAC will alter operation of the unit in an attempt to change the temperature and humidity of the air entering the unit to align with the setpoints for that unit.
For reliability, most data centers are designed with an excess number of HVAC units. Since the open-plan construction allows free flow of air throughout the data center, the operation of one unit can be coupled to the operation of another unit. The excess units and the fact that they deliver air to substantially overlapping areas provides a redundancy, which ensures that if a single unit fails, the data center equipment (servers, routers, etc.) will still have adequate cooling.
However, such redundant operation with units that operate to control air returning or discharging from a unit can cause instability in the operation of the units. For example, the intake of a first unit can be coupled to the output of another unit, thereby causing the first unit to shut off. Such problems can cause inefficient operation of the system. One solution to this problem could be not to use a discharge or return air temperature, but instead use sensors that are away from the units. But, such implementations can be costly and not practical for systems with the air temperature control already implemented.
Therefore, it is desirable to provide new systems and methods for controlling HVAC units that use a return or discharge air temperature as part of the control process.